1. Field of the Invention
The present invention relates to a low-pressure mercury vapor discharge lamp having a sealed bulb filled with a rare gas of Kr and a mercury vapor source and having a phosphor-coated inner surface, and an igniting device for generating a high-frequency output voltage.
2. Description of the Prior Art
Low-pressure mercury vapor discharge lamps which are ignited by the application of a high-frequency voltage having quiescent periods are disclosed in Japanese Utility Model Registration No. 1,400,382. The discharge lamp described therein contains a mixed gas of 25% by volume of Ne and 75% by volume of Ar sealed at 25 mm Hg and mercury vapor sealed at 6.times.10.sup.-3 mm Hg. The lamp is ignited by an electric igniting circuit composed of a four transistor bridge and an additional transistor connected in series with the bridge for applying a square-wave voltage having a duty cycle ranging from 35% to 65% to reverse the direction of current flow each time a voltage pulse is applied. When the lamp is energized at the frequency of 50 KHz and the duty cycle is 50%, the efficiency is 11% higher than when the lamp is ignited at a commercial frequency.
It is known that the recent advance of transistorized ballasts has reached the point where the electrode loss due to a discharge is reduced 10% or more when a lamp is ignited by a commercially available ballast which produces a frequency on the order of 40 KHz.
Various studies have been made in an attempt to increase the efficiency of a system in which a low-pressure mercury vapor discharge lamp and an igniting device are combined. However, the present achievement is such that no substantial increase in efficiency has been accomplished.